This invention relates to the preparation of coated, aluminum-alloy components and their installation and assembly. More specifically, the present invention relates to pre-treating surfaces of aluminum-alloy, aircraft structural components.
It has recently been discovered that the corrosion protection and ease of processing and assembly of certain, aircraft structural components can be improved by pre-treating the components with an organic, corrosion-inhibiting coating material prior to installation. It had been the conventional practice to coat such components with wet sealants that are known to require extensive and expensive special handling, especially with respect to their disposal. The pre-treatment method obviates the use of the wet sealants, reducing processing time and disposal costs. Such advances are the subject of commonly owned U.S. Pat. No. 5,614,037.
As disclosed in U.S. Pat. No. 5,614,037, it has been the practice to coat some types of fasteners in aircraft assemblies with organic coating materials to protect the base metal of the fasteners and surrounding adjacent structure against corrosion damage. In this usual approach, the fastener is first fabricated and then heat-treated to its required strength. After heat-treatment, the fastener is etched with a caustic soda bath or otherwise cleaned to remove any scale produced in the heat-treatment. The coating material, dissolved in a volatile carrier liquid, is applied to the fastener by spraying, dipping, or the like. The carrier liquid is allowed to evaporate. The coated fastener is then heated to an elevated temperature for a period of time to cure the coating; typically one hour at 400xc2x0 F. The finished fastener is then ready to be used in the assembly of the airframe structure.
This coating methodology works well with fasteners made from base metals having high melting points, such as fasteners made of steel or titanium alloys. Such fasteners are heat-treated at temperatures well above the curing temperature of the coating. Consequently, the curing process of the coating, conducted after heat-treatment of the fastener is complete, does not adversely affect the properties of the already-treated base metal.
On the other hand, non-ferrous or aluminum alloys have a much lower melting point, and generally much lower heat-treatment temperatures, than steel and titanium alloys. It has not been the practice to coat aluminum-alloy, aircraft structural components such as wing and fuselage skin panels and fasteners, etc., with curable coatings, because it is observed that the elevated temperature required to cure the coatings adversely affects the resulting strength of the components. The aluminum-alloy, aircraft structural components must therefore be protected from corrosion attack by other methods that are extremely labor intensive, such as the use of wet sealants.
The inability to pre-apply these protective coatings forces aluminum-alloy, aircraft structural components such as wing and fuselage skin panels, etc. to be installed and assembled using wet-sealant compounds for the primary purposes of corrosion protection and pressure and fuel sealing. However, the wet-sealant compounds typically contain toxic, solvent-based compounds and therefore require multiple precautions for the protection of the personnel using them as well as their safe disposal to insure environmental protection. Such wet sealants are also messy and difficult to work with. In addition, wet sealants require extensive clean-up of the area around the fastener and adjacent structure. The clean up is conducted using caustic chemical solutions after the assembly process has been completed, and therefore represents an additional and expensive manufacturing step.
Wet-sealant compounds are also applied to the faying surfaces between components throughout the aircraft. For the purpose of this application, it is understood that xe2x80x9cfaying surfacesxe2x80x9d are the interfaces of abutting or mating components that become so intimately and permanently fitted in relation to one another that the point of interface is virtually undetectable after assembly. The use of wet-sealant compounds on the faying surfaces of larger aircraft structural components results in additional waste, excessive application and clean-up time, toxic waste disposal complications, and increased cost.
There exists a need for an improved approach for the protection of the faying surfaces of these aluminum-alloy, aircraft structural components such as wing and fuselage skin panels, stiffeners (which include but are not limited to spars, ribs, stringers, longerons, frames, shear clips, xe2x80x9cbutterflyxe2x80x9d clips, etc.), hinges, doors, etc., and the mechanical components attached to these aforementioned components. Furthermore, there exists a need for improving the delivery methods and systems of such coatings onto the aluminum-alloy, aircraft structural components, including relatively large, surface-area components.
It has now been discovered that the surfaces of aluminum-alloy, aircraft structural parts can be pre-treated in order to enhance processing of the critical faying surfaces while also improving corrosion protection, reducing or eliminating cleaning and other processing steps. In addition, the improved method of applying multiple pretreatment coatings to aluminum-alloy, aircraft structural components of the present invention allows for significant processing advantages in terms of improved coating thickness tolerances and uniformity, part storage, general handling, installation, and assembly.
The present invention provides a method for preparing and treating the surfaces of aluminum-alloy, aircraft structural components such as wing and fuselage skin panels, components collectively referred to as stiffeners, hinges, doors, etc., and the mechanical components attached to these aforementioned components. In addition, the present invention is particularly applicable for the improved processing of the faying surfaces of these aircraft components. The application of the coating utilizing this method does not either alter or affect the mechanical or metallurgical properties or performance of the components and does not adversely affect the desired, final performance of the assembled aircraft structure.
In accordance with one embodiment, the present invention comprises a method for preparing an aluminum-alloy, aircraft structural component providing an artificially-aged, aluminum-alloy precursor following solution heat-treatment that is not in its final heat-treated state and coating the precursor with a first organic coating. Optionally, an encapsulated, second coating is then applied to the first coating. The twice-coated component is then precipitation heat-treated, and placed into assembly position and assembled. Encapsulant should be a material that when either squeezed or crushed is of a chemical structure such that it becomes an integral part of the adhesive which it is encapsulating.
In a further embodiment, the present invention comprises providing a naturally-aged, aluminum-alloy, aircraft structural component and coating the component with a first coating. The once-coated component is subjected to an elevated or room temperature to cure the coating. A second coating is provided in an encapsulated state and applied onto the first coating. The twice-coated component is then subjected to an elevated or room temperature environment to cure the second coating. The component is then placed into assembly position and contacted to a second component by applying a temperature or pressure change such as a compressive assembly force sufficient to liberate the second coating from its encapsulated state thereby creating a bonded interface between components.
In yet another embodiment, the present invention comprises providing a naturally-aged, aluminum-alloy, aircraft structural component and coating the component with a first coating. Optionally, a second coating is provided in an encapsulated state and applied onto the first coating. The coated component is then subjected to an elevated temperature environment to cure the coating. The component is then placed into assembly position and contacted to a second component by applying rupture conditions such as a compressive assembly force sufficient to liberate the second coating from its encapsulated state thereby creating a bonded interface between component and coating.
In yet a further embodiment, the present invention comprises providing either an artificially-aged or a naturally-aged, aluminum-alloy, aircraft structural component, coating the component with a first coating, followed optionally by applying an encapsulated, second coating. A protective release paper is then provided to the component to cover the encapsulated, coating layer prior to assembly.
Still further, the present invention comprises providing an artificially-aged, aluminum-alloy, aircraft structural component following solution heat-treatment that is not in its final heat-treated state. A first organic coating is applied to the component, followed by precipitation heat-treating the coated component. The coated component is then coated with an encapsulated, second coating. The coated component is then subjected to either an elevated or room temperature environment to cure the second coating. The twice-coated component is then placed into assembly position and contacted to a second component with a compressive assembly force applied sufficient to liberate the second coating from its encapsulated state thereby creating a bonded interface between component and coatings.
In still a further embodiment, the present invention contemplates providing an artificially-aged, aluminum-alloy, aircraft structural component in its final heat-treated state. A first coating is applied to the component optionally followed by applying an encapsulated, second coating. The component is then subjected to an elevated temperature environment to cure the two coatings. A protective release paper designed to protect the twice-coated component is optionally applied to the surface of the twice-coated component. The component is then placed into assembly ready position, the protective release paper is removed exposing the second coating. The component is then contacted to another component for final assembly. The coated component is then compressed against a second structural component in its final assembly position. The assembly compression force is sufficient to rupture the adhesive encapsulations contained in the second coating material. The second coating material reacts between the first coating and the adjacent, second structural component to enhance the overall adherence of the surface of the first component with that of the second component. The second coating material provides an enhanced bond between the faying surface of the two structural components.
In yet another embodiment, an artificially-aged, aluminum-alloy, aircraft structural component is provided in its final heat-treated state. A first coating is applied followed by either a room temperature or elevated temperature exposure to cure the first coating. A second coating is then applied to the once-coated component followed by either a room temperature or elevated temperature exposure to cure the second coating. Release paper is then optionally applied to the second coating and removed prior to assembling the component on the airframe.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.